Method and apparatus for encoding video and method and apparatus for decoding video by considering skip and split order

ABSTRACT

A method of encoding a video includes: splitting a picture into a maximum coding unit; for the maximum coding unit, determining coding units having a tree structure including coding units of coded depths and determining encoding modes for the coding units of the coded depths by performing encoding based on coding units according to depths, the coding units according to depths obtained by hierarchically splitting the maximum coding unit as a depth deepens; and outputting information about a maximum coding unit size and, for the maximum coding unit, information indicating an order of split information and skip mode information which is selectively determined for the coding units according to depths, information about the encoding modes for the coding units of the coded depths including the split information and the skip mode information which are arranged according to the order, and encoded video data.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This is a continuation of U.S. application Ser. No. 13/005,920, filedJan. 13, 2011, which claims priority from Korean Patent Application No.10-2010-0003555, filed on Jan. 14, 2010 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

Apparatuses and methods consistent with exemplary embodiments relate toencoding and decoding a video.

2. Description of the Related Art

As hardware for reproducing and storing high resolution or high qualityvideo content is being developed and supplied, a need for a video codecfor effectively encoding or decoding the high resolution or high qualityvideo content is increasing. In a related art video codec, a video isencoded according to a limited encoding method based on a macroblockhaving a predetermined size.

SUMMARY

Exemplary embodiments provide encoding and decoding of a video byconsidering a skip and split order of a coding unit according tocharacteristics of a data unit.

According to an aspect of an exemplary embodiment, there is provided amethod of encoding a video by considering a skip and split order, themethod including: splitting a picture into a maximum coding unitincluding coding units being data units in which the picture is encoded;for the maximum coding unit, determining coding units having a treestructure including coding units of coded depths and determiningencoding modes for the coding units of coded depths by performingencoding based on coding units according to depths, the coding unitsaccording to depths obtained by hierarchically splitting the maximumcoding unit as a depth deepens and the depths being proportional to anumber of times the maximum coding unit is split; and outputtinginformation about a maximum coding unit size and, for the maximum codingunit, information indicating an order of split information and skip modeinformation which is selectively determined for the coding unitsaccording to depths, information about the encoding modes for the codingunits of the coded depths including the split information and the skipmode information which are arranged according to the order, and encodedvideo data.

A coding unit may be characterized by a maximum size and a depth. Thedepth denotes the number of times a coding unit is hierarchically split,and as the depth deepens, deeper coding units according to depths may besplit from a maximum coding unit to a minimum coding unit. A depth ofthe maximum coding unit may be an uppermost depth, and a depth of theminimum coding unit may be a lowermost depth. Since sizes of codingunits according to depths decrease as the depth of the maximum codingunit deepens, a coding unit of an upper depth may include a plurality ofcoding units of lower depths.

According to a maximum size of a coding unit, image data of a currentpicture may be split into maximum coding units, and each of the maximumcoding units may include coding units split according to depths. Since amaximum coding unit is split according to depths, image data of aspatial domain included in the maximum coding unit may be hierarchicallyclassified according to depths.

A maximum depth and a maximum size of a coding unit, which limit a totalnumber of times a height and a width of the maximum coding unit arehierarchically split, may be predetermined.

The order of the split information and the skip mode information whichis selectively determined for the coding units according to depths maybe determined by at least one of an image sequence to which the codingunits according to depths belong, a slice, a slice type according to aprediction direction, and a quantization parameter of a data unit.

The order of the split information and the skip mode information whichis selectively determined for the coding units according to depths maybe determined by the depths of the coding units in the maximum codingunit.

The order of the split information and the skip mode information of thecoding units according to depths may be determined in such a manner thatif a coding unit is the maximum coding unit, the skip mode informationprecedes the split information, and if the coding unit is not themaximum coding unit, the split information precedes the skip modeinformation.

According to an aspect of another exemplary embodiment, there isprovided a method of decoding a video by considering a skip and splitorder, the method including: receiving and parsing a bitstream ofencoded video data; extracting, from the bitstream, information about amaximum size of a coding unit being a data unit in which a picture isdecoded, information about an order of split information and skip modeinformation about coding units according to depths, and, according tothe order of the split information and the skip mode information,information about a coded depth and an encoding mode and encoded videodata according to a maximum coding unit of the picture; and based on theextracted information about the maximum size of the coding unit and theinformation about the coded depth and the encoding mode, decoding theencoded video data of the picture according to coding units having atree structure including coding units of coded depths.

The extracting may include: if a coding unit is the maximum coding unit,according to the order of the split information and the skip modeinformation, determining whether the maximum coding unit is predicted ina skip mode according to the skip mode information before determiningwhether the maximum coding unit is split according to the splitinformation; if the coding unit is not the maximum coding unit,determining whether the coding unit is split according to the splitinformation before determining whether the coding unit is predicted in askip mode according to the skip mode information; and extracting theinformation about the coded depth and the encoding mode of the codeddepth and the encoded video data according to coding units of the codeddepth.

In the extracting, if one piece of split and skip information obtainedby combining the split information and the skip mode information forcoding unit according to depths is extracted, the coding units accordingto depths may be predicted in a skip mode without being split, and ifthe split information or the skip mode information for the coding unitsaccording to depths is extracted, the coding units according to depthsmay not be split or may not be predicted in a skip mode.

According to an aspect of another exemplary embodiment, there isprovided an apparatus for encoding a video by considering a skip andsplit order, the apparatus including: a maximum coding unit splitterwhich splits a picture into a maximum coding unit, including codingunits being data units in which the picture is encoded; a coding unitand encoding mode determiner which, for the maximum coding unit,determines coding units having a tree structure including coding unitsof coded depths and determines encoding modes for the coding units ofthe coded depths by performing encoding based on the coding unitsaccording to depths, the coding units according to depths obtained byhierarchically splitting the maximum coding unit as a depth deepens; andan output unit which outputs information about a maximum coding unitsize and, for the maximum coding unit, information indicating an orderof split information and skip mode information which is selectivelydetermined for the coding units according to depths, information aboutthe encoding modes of the coding units of the coded depths including thesplit information and the skip mode information which are arrangedaccording to the order, and encoded video data.

According to an aspect of another exemplary embodiment, there isprovided an apparatus for decoding a video by considering a skip andsplit order, the apparatus including: a receiver which receives andparses a bitstream of encoded video data; a data extractor whichextracts, from the bitstream, information about a maximum size of acoding unit being a data unit in which a picture is decoded, informationabout an order of split information and skip mode information of codingunits according to depths, and, according to the order of the splitinformation and the skip mode information, information about a codeddepth and an encoding mode according to a maximum coding unit of thepicture; and a decoder which, based on the information about the maximumsize of the coding unit and the information about the coded depth andthe encoding mode, decodes the encoded video data of the pictureaccording to coding units having a tree structure including coding unitsof coded depths.

According to an aspect of another exemplary embodiment, there isprovided a computer-readable recording medium having embodied thereon aprogram for executing the encoding method. Also, according to an aspectof another exemplary embodiment, there is provided a computer-readablerecording medium having embodied thereon a program for executing thedecoding method.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects will become more apparent by describing indetail exemplary embodiments with reference to the attached drawings inwhich:

FIG. 1 is a block diagram of an apparatus for encoding a video,according to an exemplary embodiment;

FIG. 2 is a block diagram of an apparatus for decoding a video,according to an exemplary embodiment;

FIG. 3 is a diagram for describing a concept of coding units accordingto an exemplary embodiment;

FIG. 4 is a block diagram of an image encoder based on coding unitsaccording to an exemplary embodiment;

FIG. 5 is a block diagram of an image decoder based on coding unitsaccording to an exemplary embodiment;

FIG. 6 is a diagram illustrating deeper coding units according todepths, and a prediction unit according to an exemplary embodiment;

FIG. 7 is a diagram for describing a relationship between a coding unitand transformation units, according to an exemplary embodiment;

FIG. 8 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment;

FIG. 9 is a diagram of deeper coding units according to depths,according to an exemplary embodiment;

FIGS. 10 through 12 are diagrams for describing a relationship betweencoding units, prediction units, and transformation units, according toan exemplary embodiment;

FIG. 13 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1;

FIG. 14 is a flowchart illustrating a method of encoding a video,according to an exemplary embodiment;

FIG. 15 is a flowchart illustrating a method of decoding a video,according to an exemplary embodiment;

FIG. 16 is a block diagram illustrating an apparatus for encoding avideo by considering a skip and split order, according to an exemplaryembodiment;

FIG. 17 is a block diagram illustrating an apparatus for decoding avideo by considering a skip and split order, according to an exemplaryembodiment;

FIG. 18 illustrates coding units according to coded depths in a maximumcoding unit, according to an exemplary embodiment;

FIGS. 19 through 21 are flowcharts illustrating methods of encoding anddecoding skip information and split information, according to variousexemplary embodiments;

FIG. 22 is a flowchart illustrating a method of encoding a video byconsidering a skip and split order, according to an exemplaryembodiment; and

FIG. 23 is a flowchart illustrating a method of decoding a video byconsidering a skip and split order, according to an exemplaryembodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

An apparatus for encoding a video, an apparatus for decoding a video, amethod of encoding a video, and a method of decoding a video accordingto exemplary embodiments will be explained with reference to FIGS. 1through 23. Encoding and decoding of a video based on a spatiallyhierarchical data unit according to one or more exemplary embodimentswill be explained with reference to FIGS. 1 through 15, and encoding anddecoding of a video considering an order of skip and split according toone or more exemplary embodiments will be explained with reference toFIGS. 16 through 23.

Exemplary embodiments will now be described more fully with reference tothe accompanying drawings.

Hereinafter, a ‘coding unit’ is an encoding data unit in which the imagedata is encoded at an encoder side, for example an encoding apparatusincluding a processor and an encoder, and an encoded data unit in whichthe encoded image data is decoded at a decoder side, for example adecoding apparatus including a processor and a decoder, according to theexemplary embodiments.

Hereinafter, an ‘image’ may denote a still image for a video or a movingimage, that is, the video itself.

An apparatus for encoding a video, an apparatus for decoding a video, amethod of encoding a video, and a method of decoding a video accordingto exemplary embodiments will be explained with reference to FIGS. 1through 15.

FIG. 1 is a block diagram of an apparatus 100 for encoding a video,according to an exemplary embodiment.

The apparatus 100 includes a maximum coding unit splitter 110, a codingunit determiner 120, and an output unit 130.

The maximum coding unit splitter 110 may split a current picture basedon a maximum coding unit for the current picture of an image. If thecurrent picture is larger than the maximum coding unit, image data ofthe current picture may be split into the at least one maximum codingunit. The maximum coding unit according to an exemplary embodiment maybe a data unit having a size of 32×32, 64×64, 128×128, 256×256, etc.,wherein a shape of the data unit is a square having a width and lengthin squares of 2. The image data may be output to the coding unitdeterminer 120 according to the at least one maximum coding unit.

A coding unit according to an exemplary embodiment may be characterizedby a maximum size and a depth. The depth denotes a number of times thecoding unit is spatially split from the maximum coding unit, and as thedepth deepens or increases, deeper coding units according to depths maybe split from the maximum coding unit to a minimum coding unit. A depthof the maximum coding unit is an uppermost depth and a depth of theminimum coding unit is a lowermost depth. Since a size of a coding unitcorresponding to each depth decreases as the depth of the maximum codingunit deepens, a coding unit corresponding to an upper depth may includea plurality of coding units corresponding to lower depths.

As described above, the image data of the current picture is split intothe maximum coding units according to a maximum size of the coding unit,and each of the maximum coding units may include deeper coding unitsthat are split according to depths. Since the maximum coding unitaccording to an exemplary embodiment is split according to depths, theimage data of a spatial domain included in the maximum coding unit maybe hierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the maximum coding unitare hierarchically split may be predetermined.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the maximum coding unit according todepths, and determines a depth to output a finally encoded image dataaccording to the at least one split region. In other words, the codingunit determiner 120 determines a coded depth by encoding the image datain the deeper coding units according to depths, according to the maximumcoding unit of the current picture, and selecting a depth having theleast encoding error. Thus, the encoded image data of the coding unitcorresponding to the determined coded depth are finally output. Also,the coding units corresponding to the coded depth may be regarded asencoded coding units.

The determined coded depth and the encoded image data according to thedetermined coded depth are output to the output unit 130.

The image data in the maximum coding unit is encoded based on the deepercoding units corresponding to at least one depth equal to or below themaximum depth, and results of encoding the image data are compared basedon each of the deeper coding units. A depth having the least encodingerror may be selected after comparing encoding errors of the deepercoding units. At least one coded depth may be selected for each maximumcoding unit.

The size of the maximum coding unit is split as a coding unit ishierarchically split according to depths, and as the number of codingunits increases. Also, even if coding units corresponding to same depthin one maximum coding unit, each of the coding units corresponding tothe same depth may be split to a lower depth by measuring an encodingerror of the image data of the each coding unit, separately.Accordingly, even when image data is included in one maximum codingunit, the image data is split to regions according to the depths, theencoding errors may differ according to regions in the one maximumcoding unite, and thus the coded depths may differ according to regionsin the image data. Thus, one or more coded depths may be determined inone maximum coding unit, and the image data of the maximum coding unitmay be divided according to coding units of at least one coded depth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the maximum coding unit. The ‘codingunits having a tree structure’ according to an exemplary embodimentinclude coding units corresponding to a depth determined to be the codeddepth, from among all deeper coding units included in the maximum codingunit. A coding unit of a coded depth may be hierarchically determinedaccording to depths in the same region of the maximum coding unit, andmay be independently determined in different regions. Similarly, a codeddepth in a current region may be independently determined from a codeddepth in another region.

A maximum depth according to an exemplary embodiment is an index relatedto the number of splitting times from a maximum coding unit to a minimumcoding unit. A first maximum depth according to an exemplary embodimentmay denote the total number of splitting times from the maximum codingunit to the minimum coding unit. A second maximum depth according to anexemplary embodiment may denote the total number of depth levels fromthe maximum coding unit to the minimum coding unit. For example, when adepth of the maximum coding unit is 0, a depth of a coding unit, inwhich the maximum coding unit is split once, may be set to 1, and adepth of a coding unit, in which the maximum coding unit is split twice,may be set to 2. Here, if the minimum coding unit is a coding unit inwhich the maximum coding unit is split four times, 5 depth levels ofdepths 0, 1, 2, 3 and 4 exist, and thus the first maximum depth may beset to 4, and the second maximum depth may be set to 5.

Prediction encoding and transformation may be performed according to themaximum coding unit. The prediction encoding and the transformation arealso performed based on the deeper coding units according to a depthequal to or depths less than the maximum depth, according to the maximumcoding unit. Transformation may be performed according to method oforthogonal transformation or integer transformation.

Since the number of deeper coding units increases whenever the maximumcoding unit is split according to depths, encoding including theprediction encoding and the transformation is performed on all of thedeeper coding units generated as the depth deepens. For convenience ofdescription, the prediction encoding and the transformation will now bedescribed based on a coding unit of a current depth, in a maximum codingunit.

The apparatus 100 may variably select a size or shape of a data unit forencoding the image data. In order to encode the image data, operations,such as prediction encoding, transformation, and entropy encoding, areperformed, and at this time, the same data unit may be used for alloperations or different data units may be used for each operation.

For example, the apparatus 100 may select not only a coding unit forencoding the image data, but also a data unit different from the codingunit so as to perform the prediction encoding on the image data in thecoding unit.

In order to perform prediction encoding in the maximum coding unit, theprediction encoding may be performed based on a coding unitcorresponding to a coded depth, i.e., based on a coding unit that is nolonger split to coding units corresponding to a lower depth.Hereinafter, the coding unit that is no longer split and becomes a basisunit for prediction encoding will now be referred to as a ‘predictionunit’. A partition obtained by splitting the prediction unit may includea data unit obtained by splitting at least one of a height and a widthof the prediction unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split and becomes a prediction unit of 2N×2N, and a size ofa partition may be 2N×2N, 2N×N, N×2N, or N×N. Examples of a partitiontype include symmetrical partitions that are obtained by symmetricallysplitting a height or width of the prediction unit, partitions obtainedby asymmetrically splitting the height or width of the prediction unit,such as 1:n or n:1, partitions that are obtained by geometricallysplitting the prediction unit, and partitions having arbitrary shapes.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. Also, the skip mode may be performed only on the partition of2N×2N. The encoding is independently performed on one prediction unit ina coding unit, thereby selecting a prediction mode having a leastencoding error.

The apparatus 100 may also perform the transformation on the image datain a coding unit based not only on the coding unit for encoding theimage data, but also based on a data unit that is different from thecoding unit.

In order to perform the transformation in the coding unit, thetransformation may be performed based on a data unit having a sizesmaller than or equal to the coding unit. For example, the data unit forthe transformation may include a data unit for an intra mode and a dataunit for an inter mode.

A data unit used as a base of the transformation will now be referred toas a ‘transformation unit’. A transformation depth indicating the numberof splitting times to reach the transformation unit by splitting theheight and width of the coding unit may also be set in thetransformation unit. For example, in a current coding unit of 2N×2N, atransformation depth may be 0 when the size of a transformation unit isalso 2N×2N, may be 1 when each of the height and width of the currentcoding unit is split into two equal parts, totally split into 4¹transformation units, and the size of the transformation unit is thusN×N, and may be 2 when each of the height and width of the currentcoding unit is split into four equal parts, totally split into 4²transformation units and the size of the transformation unit is thusN/2×N/2. For example, the transformation unit may be set according to ahierarchical tree structure, in which a transformation unit of an uppertransformation depth is split into four transformation units of a lowertransformation depth according to the hierarchical characteristics of atransformation depth.

Similarly to the coding unit, the transformation unit in the coding unitmay be recursively split into smaller sized regions, so that thetransformation unit may be determined independently in units of regions.Thus, residual data in the coding unit may be divided according to thetransformation having the tree structure according to transformationdepths.

Encoding information according to coding units corresponding to a codeddepth requires not only information about the coded depth, but alsoinformation related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a codeddepth having a least encoding error, but also determines a partitiontype in a prediction unit, a prediction mode according to predictionunits, and a size of a transformation unit for transformation.

Coding units according to a tree structure in a maximum coding unit anda method of determining a partition, according to exemplary embodiments,will be described in detail later with reference to FIGS. 3 through 12.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion Optimizationbased on Lagrangian multipliers.

The output unit 130 outputs the image data of the maximum coding unit,which is encoded based on the at least one coded depth determined by thecoding unit determiner 120, and information about the encoding modeaccording to the coded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the encoding mode according to coded depth mayinclude information about the coded depth, about the partition type inthe prediction unit, the prediction mode, and the size of thetransformation unit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth,image data in the current coding unit is encoded and output, and thusthe split information may be defined not to split the current codingunit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for onemaximum coding unit, and information about at least one encoding mode isdetermined for a coding unit of a coded depth, information about atleast one encoding mode may be determined for one maximum coding unit.Also, a coded depth of the image data of the maximum coding unit may bedifferent according to locations since the image data is hierarchicallysplit according to depths, and thus information about the coded depthand the encoding mode may be set for the image data.

Accordingly, the output unit 130 may assign encoding information about acorresponding coded depth and an encoding mode to at least one of thecoding unit, the prediction unit, and a minimum unit included in themaximum coding unit.

The minimum unit according to an exemplary embodiment is a rectangulardata unit obtained by splitting the minimum coding unit constituting thelowermost depth by 4. Alternatively, the minimum unit may be a maximumrectangular data unit that may be included in all of the coding units,prediction units, partition units, and transformation units included inthe maximum coding unit.

For example, the encoding information output through the output unit 130may be classified into encoding information according to coding units,and encoding information according to prediction units. The encodinginformation according to the coding units may include the informationabout the prediction mode and about the size of the partitions. Theencoding information according to the prediction units may includeinformation about an estimated direction of an inter mode, about areference image index of the inter mode, about a motion vector, about achroma component of an intra mode, and about an interpolation method ofthe intra mode. Also, information about a maximum size of the codingunit defined according to pictures, slices, or GOPs, and informationabout a maximum depth may be inserted into SPS (Sequence Parameter Set)or a header of a bitstream.

In the apparatus 100, the deeper coding unit may be a coding unitobtained by dividing a height or width of a coding unit of an upperdepth by two. In other words, when the size of the coding unit of thecurrent depth is 2N×2N, the size of the coding unit of the lower depthis N×N. Also, the coding unit of the current depth having the size of2N×2N may include maximum 4 of the coding unit of the lower depth.

Accordingly, the apparatus 100 may form the coding units having the treestructure by determining coding units having an optimum shape and anoptimum size for each maximum coding unit, based on the size of themaximum coding unit and the maximum depth determined consideringcharacteristics of the current picture. Also, since encoding may beperformed on each maximum coding unit by using any one of variousprediction modes and transformations, an optimum encoding mode may bedetermined considering characteristics of the coding unit of variousimage sizes.

Thus, if an image having high resolution or large data amount is encodedin a conventional macroblock, a number of macroblocks per pictureexcessively increases. Accordingly, a number of pieces of compressedinformation generated for each macroblock increases, and thus it isdifficult to transmit the compressed information and data compressionefficiency decreases. However, by using the apparatus 100, imagecompression efficiency may be increased since a coding unit is adjustedwhile considering characteristics of an image while increasing a maximumsize of a coding unit while considering a size of the image.

FIG. 2 is a block diagram of an apparatus 200 for decoding a video,according to an exemplary embodiment.

The apparatus 200 includes a receiver 210, an image data and encodinginformation extractor 220, and an image data decoder 230. Definitions ofvarious terms, such as a coding unit, a depth, a prediction unit, atransformation unit, and information about various encoding modes, forvarious operations of the apparatus 200 are identical to those describedwith reference to FIG. 1 and the apparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each maximum codingunit, and outputs the extracted image data to the image data decoder230. The image data and encoding information extractor 220 may extractinformation about a maximum size of a coding unit of a current picture,from a header about the current picture or SPS.

Also, the image data and encoding information extractor 220 extractsinformation about a coded depth and an encoding mode for the codingunits having a tree structure according to each maximum coding unit,from the parsed bitstream. The extracted information about the codeddepth and the encoding mode is output to the image data decoder 230. Inother words, the image data in a bit stream is split into the maximumcoding unit so that the image data decoder 230 decodes the image datafor each maximum coding unit.

The information about the coded depth and the encoding mode according tothe maximum coding unit may be set for information about at least onecoding unit corresponding to the coded depth, and information about anencoding mode may include information about a partition type of acorresponding coding unit corresponding to the coded depth, about aprediction mode, and a size of a transformation unit. Also, splittinginformation according to depths may be extracted as the informationabout the coded depth.

The information about the coded depth and the encoding mode according toeach maximum coding unit extracted by the image data and encodinginformation extractor 220 is information about a coded depth and anencoding mode determined to generate a minimum encoding error when anencoder, such as the apparatus 100, repeatedly performs encoding foreach deeper coding unit according to depths according to each maximumcoding unit. Accordingly, the apparatus 200 may restore an image bydecoding the image data according to a coded depth and an encoding modethat generates the minimum encoding error.

Since encoding information about the coded depth and the encoding modemay be assigned to a predetermined data unit from among a correspondingcoding unit, a prediction unit, and a minimum unit, the image data andencoding information extractor 220 may extract the information about thecoded depth and the encoding mode according to the predetermined dataunits. The predetermined data units to which the same information aboutthe coded depth and the encoding mode is assigned may be inferred to bethe data units included in the same maximum coding unit.

The image data decoder 230 restores the current picture by decoding theimage data in each maximum coding unit based on the information aboutthe coded depth and the encoding mode according to the maximum codingunits. In other words, the image data decoder 230 may decode the encodedimage data based on the extracted information about the partition type,the prediction mode, and the transformation unit for each coding unitfrom among the coding units having the tree structure included in eachmaximum coding unit. A decoding process may include a predictionincluding intra prediction and motion compensation, and a inversetransformation. Inverse transformation may be performed according tomethod of inverse orthogonal transformation or inverse integertransformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

Also, the image data decoder 230 may perform inverse transformationaccording to each transformation unit in the coding unit, based on theinformation about the size of the transformation unit of the coding unitaccording to coded depths, so as to perform the inverse transformationaccording to maximum coding units.

The image data decoder 230 may determine at least one coded depth of acurrent maximum coding unit by using split information according todepths. If the split information indicates that image data is no longersplit in the current depth, the current depth is a coded depth.Accordingly, the image data decoder 230 may decode encoded data of atleast one coding unit corresponding to the each coded depth in thecurrent maximum coding unit by using the information about the partitiontype of the prediction unit, the prediction mode, and the size of thetransformation unit for each coding unit corresponding to the codeddepth, and output the image data of the current maximum coding unit.

In other words, data units containing the encoding information includingthe same split information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same encoding mode.

The apparatus 200 may obtain information about at least one coding unitthat generates the minimum encoding error when encoding is recursivelyperformed for each maximum coding unit, and may use the information todecode the current picture. In other words, the coding units having thetree structure determined to be the optimum coding units in each maximumcoding unit may be decoded. Also, the maximum size of coding unit isdetermined considering resolution and a amount of image data.

Accordingly, even if image data has high resolution and a large amountof data, the image data may be efficiently decoded and restored by usinga size of a coding unit and an encoding mode, which are adaptivelydetermined according to characteristics of the image data, by usinginformation about an optimum encoding mode received from an encoder.

A method of determining coding units having a tree structure, aprediction unit, and a transformation unit, according to an exemplaryembodiment, will now be described with reference to FIGS. 3 through 13.

FIG. 3 is a diagram for describing a concept of coding units accordingto an exemplary embodiment.

A size of a coding unit may be expressed in width×height, and may be64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split intopartitions of 64×64, 64×32, 32×64, or 32×32, and a coding unit of 32×32may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a codingunit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8,and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8,or 4×4.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth shown inFIG. 3 denotes a total number of splits from a maximum coding unit to aminimum decoding unit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havingthe higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe video data 310 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32 and 16 sincedepths are deepened to two layers by splitting the maximum coding unittwice. Meanwhile, since the maximum depth of the video data 330 is 1,coding units 335 of the video data 330 may include a maximum coding unithaving a long axis size of 16, and coding units having a long axis sizeof 8 since depths are deepened to one layer by splitting the maximumcoding unit once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32, 16, and 8since the depths are deepened to 3 layers by splitting the maximumcoding unit three times. As a depth deepens, detailed information may beprecisely expressed.

FIG. 4 is a block diagram of an image encoder 400 based on coding units,according to an exemplary embodiment.

The image encoder 400 performs operations of the coding unit determiner120 of the apparatus 100 to encode image data. In other words, an intrapredictor 410 performs intra prediction on coding units in an intramode, from among a current frame 405, and a motion estimator 420 and amotion compensator 425 performs inter estimation and motion compensationon coding units in an inter mode from among the current frame 405 byusing the current frame 405, and a reference frame 495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as a quantized transformationcoefficient through a transformer 430 and a quantizer 440. The quantizedtransformation coefficient is restored as data in a spatial domainthrough an inverse quantizer 460 and an inverse transformer 470, and therestored data in the spatial domain is output as the reference frame 495after being post-processed through a deblocking unit 480 and a loopfiltering unit 490. The quantized transformation coefficient may beoutput as a bitstream 455 through an entropy encoder 450.

In order for the image encoder 400 to be applied in the apparatus 100,all elements of the image encoder 400, i.e., the intra predictor 410,the motion estimator 420, the motion compensator 425, the transformer430, the quantizer 440, the entropy encoder 450, the inverse quantizer460, the inverse transformer 470, the deblocking unit 480, and the loopfiltering unit 490 perform operations based on each coding unit fromamong coding units having a tree structure while considering the maximumdepth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 determines partitions and a prediction mode ofeach coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentmaximum coding unit, and the transformer 430 determines the size of thetransformation unit in each coding unit from among the coding unitshaving a tree structure.

FIG. 5 is a block diagram of an image decoder 500 based on coding units,according to an exemplary embodiment.

A parser 510 parses encoded image data to be decoded and informationabout encoding required for decoding from a bitstream 505. The encodedimage data is output as inverse quantized data through an entropydecoder 520 and an inverse quantizer 530, and the inverse quantized datais restored to image data in a spatial domain through an inversetransformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

The image data in the spatial domain, which passed through the intrapredictor 550 and the motion compensator 560, may be output as arestored frame 595 after being post-processed through a deblocking unit570 and a loop filtering unit 580. Also, the image data that ispost-processed through the deblocking unit 570 and the loop filteringunit 580 may be output as the reference frame 585.

In order to decode the image data in the image data decoder 230 of theapparatus 200, the image decoder 500 may perform operations that areperformed after the parser 510.

In order for the image decoder 500 to be applied in the apparatus 200,all elements of the image decoder 500, i.e., the parser 510, the entropydecoder 520, the inverse quantizer 530, the inverse transformer 540, theintra predictor 550, the motion compensator 560, the deblocking unit570, and the loop filtering unit 580 perform operations based on codingunits having a tree structure for each maximum coding unit.

Specifically, the intra predictor 550 and the motion compensator 560perform operations based on partitions and a prediction mode for each ofthe coding units having a tree structure, and the inverse transformer540 perform operations based on a size of a transformation unit for eachcoding unit.

FIG. 6 is a diagram illustrating deeper coding units according todepths, and partitions, according to an exemplary embodiment.

The apparatus 100 and the apparatus 200 use hierarchical coding units soas to consider characteristics of an image. A maximum height, a maximumwidth, and a maximum depth of coding units may be adaptively determinedaccording to the characteristics of the image, or may be differently setby a user. Sizes of deeper coding units according to depths may bedetermined according to the predetermined maximum size of the codingunit.

In a hierarchical structure 600 of coding units, according to anexemplary embodiment, the maximum height and the maximum width of thecoding units are each 64, and the maximum depth is 4. Since a depthdeepens along a vertical axis of the hierarchical structure 600, aheight and a width of the deeper coding unit are each split. Also, aprediction unit and partitions, which are bases for prediction encodingof each deeper coding unit, are shown along a horizontal axis of thehierarchical structure 600.

In other words, a coding unit 610 is a maximum coding unit in thehierarchical structure 600, wherein a depth is 0 and a size, i.e., aheight by width, is 64×64. The depth deepens along the vertical axis,and a coding unit 620 having a size of 32×32 and a depth of 1, a codingunit 630 having a size of 16×16 and a depth of 2, a coding unit 640having a size of 8×8 and a depth of 3, and a coding unit 650 having asize of 4×4 and a depth of 4 exist. The coding unit 650 having the sizeof 4×4 and the depth of 4 is a minimum coding unit.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having the size of 64×64 and the depth of 0 is aprediction unit, the prediction unit may be split into partitionsinclude in the coding unit 610, i.e. a partition 610 having a size of64×64, partitions 612 having the size of 64×32, partitions 614 havingthe size of 32×64, or partitions 616 having the size of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e., a partition 620 having a size of 32×32,partitions 622 having a size of 32×16, partitions 624 having a size of16×32, and partitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e. a partition having a size of 16×16 included in thecoding unit 630, partitions 632 having a size of 16×8, partitions 634having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e. a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

The coding unit 650 having the size of 4×4 and the depth of 4 is theminimum coding unit and a coding unit of the lowermost depth. Aprediction unit of the coding unit 650 is only assigned to a partitionhaving a size of 4×4, as opposed to being partitioned into partitions652 having a size of 4×2, partitions 654 having a size of 2×4, andpartitions 656 having a size of 2×2.

In order to determine the at least one coded depth of the coding unitsconstituting the maximum coding unit 610, the coding unit determiner 120of the apparatus 100 performs encoding for coding units corresponding toeach depth included in the maximum coding unit 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth deepens. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 are each encoded.

In order to perform encoding for a current depth from among the depth, aleast encoding error may be selected for the current depth by performingencoding for each prediction unit in the coding units corresponding tothe current depth, along the horizontal axis of the hierarchicalstructure 600. Alternatively, the minimum encoding error may be searchedfor by comparing the least encoding errors according to depths, byperforming encoding for each depth as the depth deepens along thevertical axis of the hierarchical structure 600. A depth and a partitionhaving the minimum encoding error in the coding unit 610 may be selectedas the coded depth and a partition type of the coding unit 610.

FIG. 7 is a diagram for describing a relationship between a coding unit710 and transformation units 720, according to an exemplary embodiment.

The apparatus 100 or 200 encodes or decodes an image according to codingunits having sizes smaller than or equal to a maximum coding unit foreach maximum coding unit. Sizes of transformation units fortransformation during encoding may be selected based on data units thatare not larger than corresponding coding unit.

For example, in the apparatus 100 or 200, if a size of the coding unit710 is 64×64, transformation may be performed by using thetransformation units 720 having a size of 32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the transformation on each of the transformationunits having the size of 32×32, 16×16, 8×8, and 4×4, which are smallerthan 64×64, and then a transformation unit having the least coding errormay be selected.

FIG. 8 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment.

The output unit 130 of the apparatus 100 may encode and transmitinformation 800 about a partition type, information 810 about aprediction mode, and information 820 about a size of a transformationunit for each coding unit corresponding to a coded depth, as informationabout an encoding mode.

The information 800 indicates information about a shape of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_(—)0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, a partition 806 having asize of N×2N, and a partition 808 having a size of N×N. Here, theinformation 800 about a partition type is set to indicate one of thepartition 804 having a size of 2N×N, the partition 806 having a size ofN×2N, and the partition 808 having a size of N×N

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second inter transformation unit 828.

The image data and encoding information extractor 220 of the apparatus200 may extract and use the information 800, 810, and 820 for decoding.

FIG. 9 is a diagram of deeper coding units according to depths,according to an exemplary embodiment.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_(—)0×2N_(—)0 may include partitions of apartition type 912 having a size of 2N_(—)0×2N_(—)0, a partition type914 having a size of 2N_(—)0×N_(—)0, a partition type 916 having a sizeof N_(—)0×2N_(—)0, and a partition type 918 having a size ofN_(—)0×N_(—)0. FIG. 9 only illustrates the partition types 912 through918 which are obtained by symmetrically splitting the prediction unit910, but a partition type is not limited thereto, and the partitions ofthe prediction unit 910 may include asymmetrical partitions, partitionshaving a predetermined shape, and partitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_(—)0×2N_(—)0, two partitions having a size of 2N_(—)0×N_(—)0,two partitions having a size of N_(—)0×2N_(—)0, and four partitionshaving a size of N_(—)0×N_(—)0, according to each partition type. Theprediction encoding in an intra mode and an inter mode may be performedon the partitions having the sizes of 2N_(—)0×2N_(—)0, N_(—)0×2N_(—)0,2N_(—)0×N_(—)0, and N_(—)0×N_(—)0. The prediction encoding in a skipmode is performed only on the partition having the size of2N_(—)0×2N_(—)0.

Errors of encoding including the prediction encoding in the partitiontypes 912 through 918 are compared, and the least encoding error isdetermined among the partition types. If an encoding error is smallestin one of the partition types 912 through 916, the prediction unit 910may not be split into a lower depth.

If the encoding error is the smallest in the partition type 918, a depthis changed from 0 to 1 to split the partition type 918 in operation 920,and encoding is repeatedly performed on coding units 930 having a depthof 2 and a size of N_(—)0×N_(—)0 to search for a minimum encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_(—)1×2N_(—)1 (=N_(—)0×N_(—)0) may includepartitions of a partition type 942 having a size of 2N_(—)1×2N_(—)1, apartition type 944 having a size of 2N_l×N_(—)1, a partition type 946having a size of N_(—)1×2N_(—)1, and a partition type 948 having a sizeof N_l×N_(—)1.

If an encoding error is the smallest in the partition type 948, a depthis changed from 1 to 2 to split the partition type 948 in operation 950,and encoding is repeatedly performed on coding units 960, which have adepth of 2 and a size of N_(—)2×N_(—)2 to search for a minimum encodingerror.

When a maximum depth is d, split operation according to each depth maybe performed up to when a depth becomes d−1, and split information maybe encoded as up to when a depth is one of 0 to d−2. In other words,when encoding is performed up to when the depth is d−1 after a codingunit corresponding to a depth of d−2 is split in operation 970, aprediction unit 990 for prediction encoding a coding unit 980 having adepth of d−1 and a size of 2N_(d−1)×2N_(d−1) may include partitions of apartition type 992 having a size of 2N_(d−1)×2N_(d−1), a partition type994 having a size of 2N_(d−1)×N_(d−1), a partition type 996 having asize of N_(d−1)×2N_(d−1), and a partition type 998 having a size ofN_(d−1)×N_(d−1).

Prediction encoding may be repeatedly performed on one partition havinga size of 2N_(d−1)×2N_(d−1), two partitions having a size of2N_(d−1)×N_(d−1), two partitions having a size of N_(d−1)×2N_(d−1), fourpartitions having a size of N_(d−1)×N_(d−1) from among the partitiontypes 992 through 998 to search for a partition type having a minimumencoding error.

Even when the partition type 998 has the minimum encoding error, since amaximum depth is d, a coding unit CU_(d−1) having a depth of d−1 is nolonger split to a lower depth, and a coded depth for the coding unitsconstituting a current maximum coding unit 900 is determined to be d−1and a partition type of the coding unit 900 may be determined to beN_(d−1)×N_(d−1). Also, since the maximum depth is d and a minimum codingunit 980 having a lowermost depth of d−1 is no longer split to a lowerdepth, split information for a coding unit 980 is not set.

A data unit 999 may be a ‘minimum unit’ for the current maximum codingunit. A minimum unit according to an exemplary embodiment may be arectangular data unit obtained by splitting a minimum coding unit 980 by4. By performing the encoding repeatedly, the apparatus 100 may select adepth having the least encoding error by comparing encoding errorsaccording to depths of the coding unit 900 to determine a coded depth,and set a corresponding partition type and a prediction mode as anencoding mode of the coded depth.

As such, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about an encoding mode. Also, since a codingunit is split from a depth of 0 to a coded depth, only split informationof the coded depth is set to 0, and split information of depthsexcluding the coded depth is set to 1.

The image data and encoding information extractor 220 of the apparatus200 may extract and use the information about the coded depth and theprediction unit of the coding unit 900 to decode the partition 912. Theapparatus 200 may determine a depth, in which split information is 0, asa coded depth by using split information according to depths, and useinformation about an encoding mode of the corresponding depth fordecoding.

FIGS. 10 through 12 are diagrams for describing a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070,according to an exemplary embodiment.

The coding units 1010 are coding units having a tree structure,corresponding to coded depths determined by the apparatus 100, in amaximum coding unit. The prediction units 1060 are partitions ofprediction units of each of the coding units 1010, and thetransformation units 1070 are transformation units of each of the codingunits 1010.

When a depth of a maximum coding unit is 0 in the coding units 1010,depths of coding units 1012 and 1054 are 1, depths of coding units 1014,1016, 1018, 1028, 1050, and 1052 are 2, depths of coding units 1020,1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units1040, 1042, 1044, and 1046 are 4.

In the prediction units 1060, some coding units 1014, 1016, 1022, 1032,1048, 1050, 1052, and 1054 are split into partitions for predictionencoding. In other words, partition types in the coding units 1014,1022, 1050, and 1054 have a size of 2N×N, partition types in the codingunits 1016, 1048, and 1052 have a size of N×2N, and a partition type ofthe coding unit 1032 has a size of N×N. Prediction units and partitionsof the coding units 1010 are smaller than or equal to each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. Also, the coding units 1014,1016, 1022, 1032, 1048, 1050, and 1052 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the apparatuses 100 and 200 may performintra prediction, motion estimation, motion compensation,transformation, and inverse transformation individually on a data unitin the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of a maximum coding unitto determine an optimum coding unit, and thus coding units having arecursive tree structure may be obtained. Encoding information mayinclude split information about a coding unit, information about apartition type, information about a prediction mode, and informationabout a size of a transformation unit. Table 1 shows the encodinginformation that may be set by the apparatuses 100 and 200.

TABLE 1 Split Information 0 (Encoding on Coding unit having Size of 2N ×2N and Current Depth of d) Size of Transformation Unit Split SplitPartition Type Information 0 Information 1 Symmetrical Asymmetrical ofof Prediction Partition Partition Transformation Transformation SplitMode Type Type Unit Unit Information 1 Intra 2N × 2N 2N × nU 2N × 2N N ×N Repeatedly Inter 2N × N 2N × nD (Symmetrical Encode Skip N × 2N nL ×2N Type) Coding Units (Only N × N nR × 2N N/2 × N/2 having 2N × 2N)(Asymmetrical Lower Depth Type) of d + 1

The output unit 130 of the apparatus 100 may output the encodinginformation about the coding units having a tree structure, and theimage data and encoding information extractor 220 of the apparatus 200may extract the encoding information about the coding units having atree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split into alower depth, is a coded depth, and thus information about a partitiontype, prediction mode, and a size of a transformation unit may bedefined for the coded depth. If the current coding unit is further splitaccording to the split information, encoding is independently performedon four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode is defined only in a partition type having asize of 2N×2N.

The information about the partition type may indicate symmetricalpartition types having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition types having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition typeshaving the sizes of 2N×nU and 2N×nD may be respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Also, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be N×N, and if the partition type of the currentcoding unit is an asymmetrical partition type, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structure mayinclude at least one of a coding unit corresponding to a coded depth, aprediction unit, and a minimum unit. The coding unit corresponding tothe coded depth may include at least one of a prediction unit and aminimum unit containing the same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. Also, a correspondingcoding unit corresponding to a coded depth is determined by usingencoding information of a data unit, and thus a distribution of codeddepths in a maximum coding unit may be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoded information of the data units,and the searched adjacent coding units may be referred for predictingthe current coding unit.

FIG. 13 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1.

A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312,1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318is a coding unit of a coded depth, split information may be set to 0.Information about a partition type of the coding unit 1318 having a sizeof 2N×2N may be set to be one of a partition type 1322 having a size of2N×2N, a partition type 1324 having a size of 2N×N, a partition type1326 having a size of N×2N, a partition type 1328 having a size of N×N,a partition type 1332 having a size of 2N×nU, a partition type 1334having a size of 2N×nD, a partition type 1336 having a size of nL×2N,and a partition type 1338 having a size of nR×2N.

When the partition type is set to be symmetrical, i.e. the partitiontype 1322, 1324, 1326, or 1328, a transformation unit 1342 having a sizeof 2N×2N is set if split information (TU size flag) of a transformationunit is 0, and a transformation unit 1344 having a size of N×N is set ifa TU size flag is 1.

When the partition type is set to be asymmetrical, i.e., the partitiontype 1332, 1334, 1336, or 1338, a transformation unit 1352 having a sizeof 2N×2N is set if a TU size flag is 0, and a transformation unit 1354having a size of N/2×N/2 is set if a TU size flag is 1.

Referring to FIG. 13, the TU size flag is a flag having a value or 0 or1, but the TU size flag is not limited to 1 bit, and a transformationunit may be hierarchically split having a tree structure while the TUsize flag increases from 0.

In this case, the size of a transformation unit that has been actuallyused may be expressed by using a TU size flag of a transformation unit,according to an exemplary embodiment, together with a maximum size andminimum size of the transformation unit. According to an exemplaryembodiment, the video encoding apparatus 100 is capable of encodingmaximum transformation unit size information, minimum transformationunit size information, and a maximum TU size flag. The result ofencoding the maximum transformation unit size information, the minimumtransformation unit size information, and the maximum TU size flag maybe inserted into an SPS. According to an exemplary embodiment, the videodecoding apparatus 200 may decode video by using the maximumtransformation unit size information, the minimum transformation unitsize information, and the maximum TU size flag.

For example, if the size of a current coding unit is 64×64 and a maximumtransformation unit size is 32×32, then the size of a transformationunit may be 32×32 when a TU size flag is 0, may be 16×16 when the TUsize flag is 1, and may be 8×8 when the TU size flag is 2.

As another example, if the size of the current coding unit is 32×32 anda minimum transformation unit size is 32×32, then the size of thetransformation unit may be 32×32 when the TU size flag is 0. Here, theTU size flag cannot be set to a value other than 0, since the size ofthe transformation unit cannot be less than 32×32.

As another example, if the size of the current coding unit is 64×64 anda maximum TU size flag is 1, then the TU size flag may be 0 or 1. Here,the TU size flag cannot be set to a value other than 0 or 1.

Thus, if it is defined that the maximum TU size flag is‘MaxTransformSizeIndex’, a minimum transformation unit size is‘MinTransformSize’, and a transformation unit size is ‘RootTuSize’ whenthe TU size flag is 0, then a current minimum transformation unit size‘CurrMinTuSize’ that can be determined in a current coding unit, may bedefined by Equation (1):CurrMinTuSize=max(MinTransformSize,RootTuSize/(2^MaxTransformSizeIndex))  (1)

Compared to the current minimum transformation unit size ‘CurrMinTuSize’that can be determined in the current coding unit, a transformation unitsize ‘RootTuSize’ when the TU size flag is 0 may denote a maximumtransformation unit size that can be selected in the system. In Equation(1), ‘RootTuSize/(2^MaxTransformSizeIndex)’ denotes a transformationunit size when the transformation unit size ‘RootTuSize’, when the TUsize flag is 0, is split a number of times corresponding to the maximumTU size flag, and ‘MinTransformSize’ denotes a minimum transformationsize. Thus, a smaller value from among‘RootTuSize/(2^MaxTransformSizeIndex)’ and ‘MinTransformSize’ may be thecurrent minimum transformation unit size ‘CurrMinTuSize’ that can bedetermined in the current coding unit.

According to an exemplary embodiment, the maximum transformation unitsize RootTuSize may vary according to the type of a prediction mode.

For example, if a current prediction mode is an inter mode, then‘RootTuSize’ may be determined by using Equation (2) below. In Equation(2), ‘MaxTransformSize’ denotes a maximum transformation unit size, and‘PUSize’ denotes a current prediction unit size.RootTuSize=min(MaxTransformSize,PUSize)  (2)

That is, if the current prediction mode is the inter mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0, may bea smaller value from among the maximum transformation unit size and thecurrent prediction unit size.

If a prediction mode of a current partition unit is an intra mode,‘RootTuSize’ may be determined by using Equation (3) below. In Equation(3), ‘PartitionSize’ denotes the size of the current partition unit.RootTuSize=min(MaxTransformSize,PartitionSize)  (3)

That is, if the current prediction mode is the intra mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0 may bea smaller value from among the maximum transformation unit size and thesize of the current partition unit.

However, the current maximum transformation unit size ‘RootTuSize’ thatvaries according to the type of a prediction mode in a partition unit isjust an example and is not limited thereto.

FIG. 14 is a flowchart illustrating a method of encoding a video,according to an exemplary embodiment.

In operation 1210, a current picture is split into at least one maximumcoding unit. A maximum depth indicating the total number of possiblesplitting times may be predetermined.

In operation 1220, a coded depth to output a final encoding resultaccording to at least one split region, which is obtained by splitting aregion of each maximum coding unit according to depths, is determined byencoding the at least one split region, and a coding unit according to atree structure is determined.

The maximum coding unit is spatially split whenever the depth deepens,and thus is split into coding units of a lower depth. Each coding unitmay be split into coding units of another lower depth by being spatiallysplit independently from adjacent coding units. Encoding is repeatedlyperformed on each coding unit according to depths.

Also, a transformation unit according to partition types having theleast encoding error is determined for each deeper coding unit. In orderto determine a coded depth having a minimum encoding error in eachmaximum coding unit, encoding errors may be measured and compared in alldeeper coding units according to depths.

In operation 1230, encoded image data constituting the final encodingresult according to the coded depth is output for each maximum codingunit, with encoding information about the coded depth and an encodingmode. The information about the encoding mode may include informationabout a coded depth or split information, information about a partitiontype of a prediction unit, a prediction mode, and a size of atransformation unit. The encoded information about the encoding mode maybe transmitted to a decoder with the encoded image data.

FIG. 15 is a flowchart illustrating a method of decoding a video,according to an exemplary embodiment.

In operation 1310, a bitstream of an encoded video is received andparsed.

In operation 1320, encoded image data of a current picture assigned to amaximum coding unit, and information about a coded depth and an encodingmode according to maximum coding units are extracted from the parsedbitstream. The coded depth of each maximum coding unit is a depth havingthe least encoding error for the each maximum coding unit. In encodingeach maximum coding unit, the image data is encoded based on at leastone data unit obtained by hierarchically splitting the each maximumcoding unit according to depths.

According to the information about the coded depth and the encodingmode, the maximum coding unit may be split into coding units having atree structure. Each coding unit of the coding units having the treestructure is determined as a coding unit corresponding to a coded depth,optimally encoded as to output the least encoding error. Accordingly,encoding and decoding efficiency of an image may be improved by decodingeach piece of encoded image data in the coding units after determiningat least one coded depth according to coding units.

In operation 1330, the image data of each maximum coding unit is decodedbased on the information about the coded depth and the encoding modeaccording to the maximum coding units. The decoded image data may bereproduced by a reproducing apparatus, stored in a storage medium, ortransmitted through a network.

Encoding and decoding of a video considering an order of skip and splitaccording to exemplary embodiments will now be explained with referenceto FIGS. 16 through 23.

FIG. 16 is a block diagram illustrating an apparatus 1400 for encoding avideo by considering a skip and split order, according to an exemplaryembodiment.

Referring to FIG. 16, the apparatus 1400 includes a maximum coding unitsplitter 1410, a coding unit and encoding mode determiner 1420, and anoutput unit 1430.

The apparatus 1400 of FIG. 16 may be an example of the apparatus 100 ofFIG. 1, and the maximum coding unit splitter 110, the coding unitdeterminer 120, and the output unit 130 of the apparatus 100 of FIG. 1may correspond to the maximum coding unit splitter 1410, the coding unitand encoding mode determiner 1420, and the output unit 1430 of FIG. 16,respectively.

The maximum coding unit splitter 1410 splits a picture of an input imageinto maximum coding units having predetermined sizes, and image dataaccording to the maximum coding units is output to the coding unit andencoding mode determiner 1420.

The coding unit and encoding mode determiner 1420 hierarchically splitsregions of each of the maximum coding units input from the maximumcoding unit splitter 1410 as a depth deepens, and individually performsencoding based on coding units according to depths corresponding tosplit numbers for every independent region hierarchically split. Thecoding unit and encoding mode determiner 1420 determines an encodingmode and a coded depth to output an encoding result according to eachregion. The encoding mode may include information about a partition typeof a coding unit corresponding to the coded depth, about a predictionmode, and about a size of a transformation unit.

In order to determine an encoding mode and a coded depth to output anencoding result for every independent region of a maximum coding unit,the coding unit and encoding mode determiner 1420 may perform encodingbased on coding units according to depths, and may search for a codeddepth having a least encoding error in original image data and anencoding mode related to the coded depth. Accordingly, the coding unitand encoding mode determiner 1420 may determine the coding units havingthe tree structure by determining coding units corresponding to codeddepths for each maximum coding unit of the current picture

Information about the coded depth and the encoding mode determined bythe coding unit and encoding mode determiner 1420 and a correspondingencoding result are output to the output unit 1430.

The output unit 1430 outputs information about a coded depth and anencoding mode according to a maximum coding unit, and encoded videodata. An encoding mode includes skip mode information indicating whethera prediction mode of a coding unit is a skip mode, and split informationindicating whether the coding unit is split to a lower depth. Since aprediction mode of a coding unit may be determined in a coding unit of acoded depth which is not further split, skip mode information may beencoded in the coding unit of the coded depth.

The output unit 1430 may selectively determine an order in which skipmode information and split information of coding units according todepths are output.

The output unit 1430 may output information indicating a selectivelydetermined order in which skip mode information and split informationare output. Accordingly, the output unit 1430 may output informationabout an order in which skip mode information and split information areoutput, the information about an encoding mode including the skip modeinformation and the split information which are arranged in theselectively determined order, and encoded video data.

The order of the skip mode information and the split information whichis selectively determined for every coding unit according to depths maybe determined according to at least one of an image sequence to which acoding unit corresponding to each depth belongs, a slice, a slice typeaccording to a prediction direction, and a quantization parameter (QP)of a data unit.

Also, the order of the skip mode information and the split informationwhich is selectively determined for every coding unit according todepths may be individually determined according to depths of codingunits in a maximum coding unit.

For example, the order of the skip mode information and the splitinformation may be determined in such a manner that the skip modeinformation precedes the split information for a maximum coding unit,and the split information precedes the skip mode information for codingunits of lower depths other than the maximum coding unit.

The output unit 1430 may perform encoding by combining the splitinformation and the skip mode information as one piece of split and skipinformation. Also, the output unit 1430 may assign different bit numbersto the split and skip information according to a frequency of occurrenceof a combination of the split information and the skip mode information.

For example, if both split information indicating that a correspondingcoding unit is split and skip mode information indicating that aprediction mode of the corresponding coding unit is not a skip mode areencoded, the split and skip information may be assigned one bit. Also,in cases other than the case where both the split information indicatingthat the corresponding coding unit is split and the skip modeinformation indicating that the prediction mode of the correspondingcoding unit is not the skip mode are encoded, the split and skipinformation may be assigned two bits and output.

The output unit 1430 may not encode a transformation coefficient andprediction-related information such as a prediction direction and amotion vector, for a coding unit that is predicted in a skip mode.Selectively, the output unit 1430 may encode motion vector predictorindex information about a prediction unit adjacent to a current codingunit. Also, the output unit 1430 may output information about a maximumsize of the coding units.

FIG. 17 is a block diagram illustrating an apparatus 1500 for decoding avideo by considering a skip and split order, according to an exemplaryembodiment.

Referring to FIG. 17, the apparatus 1500 includes a receiver 1510, adata extractor 1520, and a decoder 1530. The apparatus 1500 of FIG. 17may be an example of the apparatus 200 of FIG. 2. The receiver 210, theimage data and encoding information extractor 220, and the image datadecoder 230 of the apparatus 200 of FIG. 2 may correspond to thereceiver 1510, the data extractor 1520, and the decoder 1530 of theapparatus 1500 of FIG. 17, respectively.

The receiver 1510 receives and parses a bitstream of an encoded video.

The data extractor 1520 receives the parsed bitstream from the receiver1510, and extracts encoded video data and information about a codeddepth and an encoding mode for each maximum coding unit from thebitstream. Also, the data extractor 1520 may extract information about amaximum size of the coding units from the bitstream. The data extractor1520 extracts, from the bitstream, information about an order of skipmode information and split information of coding units according todepths.

The data extractor 1520 may read the skip mode information and the splitinformation from the information about the encoding mode based on theextracted information about the order of the skip mode information andthe split information, and extract the encoded video data in codingunits according to depths based on the skip mode information and thesplit information.

The order of the skip mode information and the split information may beselectively set according to at least one of an image sequence to whicha coding unit corresponding to each depth belongs, a slice, a slice typeaccording to a prediction direction, and a QP of a data unit. Also, theorder of the skip mode information and the split information may beselectively set according to depths of coding units according to depthsin a maximum coding unit.

For example, if a coding unit is a maximum coding unit, according to theorder of the skip mode information and the split information, whetherthe coding unit is predicted in a skip mode according to the skip modeinformation may be determined before determining whether the coding unitis split according to the split information. Also, if a coding unit isnot a maximum coding unit, whether the coding unit is split according tothe split information may be determined before determining whether thecoding unit is predicted in a skip mode according to the skip modeinformation.

The data extractor 1520 may extract one piece of split and skipinformation obtained by combining the skip mode information and thesplit information for the coding units according to the depths. Forexample, if one bit of split and skip information is extracted, acorresponding coding unit may be predicted in a skip mode without beingsplit, and if two bits of split and skip information is read, whether acorresponding coding unit is split may be determined based on the splitinformation and whether the corresponding coding unit is predicted in askip mode may be determined based on the skip mode information.

The data extractor 1520 may extract only the split information and theskip mode information for a coding unit that is predicted in a skipmode, and may not extract information for prediction decoding such as atransformation coefficient and prediction-related information such as aprediction direction and a motion vector. Motion vector predictor indexinformation for a coding unit that is predicted in a skip mode may beselectively extracted. Accordingly, the decoder 1530 may performprediction decoding on a current coding unit by borrowing motioninformation of a prediction unit adjacent to the current coding unitthat is predicted in a skip mode, or inferring motion information of thecurrent coding unit from motion information of the adjacent predictionunit.

The decoder 1530 decodes encoded video data according to a coding unitof at least one coded depth for every maximum coding unit of the encodedvideo data based on the information about the coded depth and theencoding mode.

Decoded and restored video data may be transmitted to various terminalswhich may reproduce the video data or may be stored in a storage device.

The apparatus 1400 of FIG. 16 and the apparatus 1500 of FIG. 17 maydetermine an order of skip mode information and split information byconsidering a data unit, an encoding mode, or the like. Also, the orderof the skip mode information and the split information may be determinedby considering a total bit number of the skip mode information and thesplit information, and a frequency of occurrence of a skip mode inencoding and decoding of video data. Since the order of the skip modeinformation and the split information of coding units according todepths may be set, encoded data transmission efficiency may be furtherimproved.

FIG. 18 illustrates coding units according to coded depths in a maximumcoding unit, according to an exemplary embodiment.

In order to explain an order in which the data extractor 1520 reads anencoded bitstream output from the output unit 1430 by considering anorder of skip mode information and split information, a maximum codingunit 1600 is exemplary illustrated.

Coding units included in the maximum coding unit 1600 include themaximum coding unit 1600 having a depth of 0, coding units 1610, 1620,1630, and 1640 having a depth of 1, and coding units 1622, 1624, 1626,and 1628 having a depth of 2. Also, the coding units 1610, 1630, and1640 having the coded depth of 1 and the coding units 1622, 1624, 1626,and 1628 having the coded depth of 2 are determined as coded depths ofthe maximum coding unit 1600. Also, it is assumed that prediction modesof the coding units 1610, 1630, and 1640 having the depth of 1 are setto skip modes, and prediction modes of the coding units 1622, 1624,1626, and 1628 having the depth of 2 are not set to skip modes.

An example where the data extractor 1520 of the apparatus 1500 readssplit information before reading skip mode information for the maximumcoding unit 1600 of a current picture will be first explained. In thisexample where the split information precedes the skip mode information,if the split information is 1, split information of coding units oflower depths is recursively read, and if the split information is 0,skip mode information of a coding unit of a corresponding depth is read.

Accordingly, an order in which split information and skip modeinformation are set or read is as follows.

Split information 1 about the maximum coding unit 1600, splitinformation 0 and skip information 1 about the coding unit 1610 havingthe depth of 1, split information 0 about the coding unit 1620 havingthe depth of 1, split information 0 and skip information 0 about thecoding unit 1622 having the depth of 2, split information 0 and the skipinformation 0 about the coding unit 1624 having the depth of 2, splitinformation 0 and skip information 0 about the coding unit 1626 havingthe depth of 2, split information 0 and skip information 0 about thecoding unit 1628 having the depth of 2, split information 0 and skipinformation 1 about the coding unit 1630 having the depth of 1, andsplit information 0 and skip information 1 about the coding unit 1640having the depth of 1 may be sequentially read. Accordingly, a total bitnumber of the split information and the skip mode information of themaximum coding unit 1600 is 16.

Also, another example where the data extractor 1520 of the apparatus1400 reads skip mode information of the maximum coding unit 1600 of acurrent picture earlier than split information will be explained. Inthis example where the skip mode information precedes the splitinformation, if the skip mode information is 1, split information ofcoding units having lower depths do not need to be set, and if the skipmode information is 0, the split information is set. Accordingly, anorder in which the split information and the skip mode information areset or read is as follows.

Skip mode information 0 about the maximum coding unit 1600, skip modeinformation 1 about the coding unit 1610 having the depth of 1, skipmode information 0 and split information 1 about the coding unit 1620having the depth of 1, skip mode information 0 and split information 0about the coding unit 1622 having the depth of 2, skip mode information0 and split information 0 about the coding unit 1624 having the depth of2, skip mode information 0 and split information 0 about the coding unit1626 having the depth of 2, skip mode information 0 and splitinformation 0 about the coding unit 1628 having the depth of 2, skipmode information 1 about the coding unit 1630 having the depth of 1, andskip mode information 1 about the coding unit 1640 having the depth of 1may be sequentially read. In this case, a total bit number of the splitinformation and the skip mode information about the maximum coding unit1600 is 14.

FIGS. 19 through 21 are flowcharts illustrating methods of encoding anddecoding skip information and split information, according to variousexemplary embodiments.

If the output unit 1430 of the apparatus 1400 outputs an encodedbitstream in such a manner that split information precedes skip modeinformation according to a split first method, the data extractor 1520of the apparatus 1500 reads encoded video data according to an order inwhich the skip mode information and the split information are read.

That is, in operation 1650, according to the split first method, thedata extractor 1520 reads split information about a maximum coding unithaving a depth of 0 and determines whether the maximum coding unit issplit. If it is determined in operation 1650 that the maximum codingunit is not split, the method proceeds to operation 1652. In operation1652, skip mode information is read and it is determined whether themaximum coding unit is predicted in a skip mode. If it is determined inoperation 1650 that the maximum coding unit is split, the methodproceeds to operation 1654. In operation 1654, split information of acoding unit having a depth of 1 is read. Similarly, in operation 1654,it is determined whether the coding unit having the depth of 1 is split.If it is determined in operation 1654 that the coding unit having thedepth of 1 is not split according to split information of the codingunit having the depth of 1, the method proceeds to operation 1656. Inoperation 1656, skip mode information of the coding unit having thedepth of 1 is read. If it is determined in operation 1654 that thecoding unit having the depth of 1 is split, the method proceeds tooperation 1658. In operation 1658, split information of a coding unithaving a depth of 2 is read and it is determined whether the coding unithaving the depth of 2 is split. If it is determined in operation 1658that the coding unit having the depth of 2 is not split, the methodproceeds to operation 1660. In operation 1660, skip mode information ofthe coding unit having the depth of 2 is read. If it is determined inoperation 1658 that the coding unit having the depth of 2 is split, themethod may proceed to a next depth.

If the output unit 1430 of the apparatus 1400 outputs an encodedbitstream in such a manner that skip mode information precedes splitinformation according to a skip first method, the data extractor 1520 ofthe apparatus 1500 reads encoded video data according to an order inwhich the skip mode information and the split information are read.

That is, in operation 1670, according to the skip first method, the dataextractor 1520 reads skip mode information about a maximum coding unithaving a depth of 0. If it is determined from the reading that aprediction mode of the maximum coding unit is a skip mode, the decoder1530 may decode the maximum coding unit in a skip mode. In operation1670, if it is determined from the reading that the prediction mode ofthe maximum coding unit is not a skip mode, the method may proceed tooperation 1672. In operation 1672, the data extractor 1520 may readsplit information of the maximum coding unit having the depth of 0. Inoperation 1672, if it is determined from the reading that the maximumcoding unit is not split, the decoder 1530 may decode the maximum codingunit. In operation 1672, if it is determined from the reading that themaximum coding unit is split, the method proceeds to operation 1674. Inoperation 1674, the data extractor 1520 may read skip mode informationof a coding unit having a depth of 1.

Similarly, in operation 1674, according to the skip mode information ofthe coding unit having the depth of 1, if it is determined from thereading that a prediction mode of the coding unit having the depth of 1is a skip mode, the coding unit having the depth of 1 may be decoded ina skip mode. If it is determined from the reading in operation 1674 thata prediction mode of the coding unit having the depth of 1 is not a skipmode, the method proceeds to operation 1676. In operation 1676, splitinformation of the coding unit having the depth of 1 may be read.

If the output unit 1430 of the apparatus 1400 performs encoding in sucha manner that skip mode information precedes split information for amaximum coding unit and split information precedes skip mode informationfor coding units other than the maximum coding unit, the data extractor1520 of the apparatus 1500 reads encoded video data according to anorder in which the skip mode information and the split information areread.

That is, in operation 1680, according to a skip first method for amaximum coding unit having a depth of 0, the data extractor 1520 readsskip mode information about the maximum coding unit having the depth of0. If it is determined from the reading that a prediction mode of themaximum coding unit is a skip mode, the decoder 1530 may decode themaximum coding unit in a skip mode. In operation 1680, if it isdetermined from the reading that the prediction mode of the maximumcoding unit is not a skip mode, the method proceeds to operation 1682.In operation 1682, the data extractor 1520 may read split information ofthe maximum coding unit having the depth of 0. In operation 1682, if itis determined from the reading that the maximum coding unit is notsplit, the decoder 1530 may decode the maximum coding unit. In operation1682, if it is determined from the reading that the maximum coding unitis split, the data extractor 1520 may read split information and skipmode information of a coding unit having a depth of 1 in operations 1684and 1686.

In operation 1684, according to a split first method for the coding unithaving the depth of 1, if it is determined from the reading that thecoding unit having the depth of 1 is not split according to splitinformation of the coding unit having the depth of 1, the methodproceeds to operation 1686. In operation 1686, skip mode information ofthe coding unit having the depth of 1 is read. In operation 1684, if itis determined from the reading that the coding unit having the depth of1 is split, the method proceeds to operation 1688, and split informationof a coding unit having a depth of 2 may be read. In operation 1688, ifthe coding unit having the depth of 2 is not split according to thesplit information of the coding unit having the depth of 2, the methodproceeds to operation 1690. In operation 1690, skip mode information ofthe coding unit having the depth of 2 may be read, and if the codingunit having the depth of 2 is split, the method may proceed to a nextdepth.

Total bit numbers of skip mode information and split informationaccording to the exemplar embodiments of FIGS. 19 through 21 will becompared with one another as follows.

In detail, if a maximum coding unit is encoded in a skip mode, total bitnumbers of skip mode information and split information according tovarious exemplary embodiments are as shown in Table 2.

TABLE 2 Skip mode information Embodiment and split information Total bitnumber Split first method (FIG. Split information 0, skip  2 bits 19)mode information 1 Skip first method (FIG. Skip mode information 1 1 bit20) Maximum coding unit Skip mode information 1 1 bit skip first method(FIG. 21)

According to a split first method of Table 2, since split information ofa maximum coding unit having a depth of 0 is encoded to be ‘0’ and skipmode information of the maximum coding unit having the depth of 0 isencoded to be ‘1’, the data extractor 1520 may read two bits of skipmode information and split information in total. According to a skipfirst method of Table 2, since skip mode information of the maximumcoding unit having the depth of 0 is encoded to be ‘1’, the dataextractor 1520 may read one bit of skip mode information in total.According to a maximum coding unit skip first method of Table 2, sinceskip mode information of the maximum coding unit having the depth of 0is encoded to be ‘1’, the data extractor 1520 may read only one bit ofskip mode information in total.

In detail, if a coding unit having a depth of 2 is encoded in a skipmode, total bit numbers of skip mode information and split informationaccording to various exemplary embodiments are as shown in Table 3.

TABLE 3 Skip mode information Embodiment and split information Total bitnumber Split first method (FIG. Split information 1, split 4 bits 19)information 1, split information 0, skip mode information 1 Skip firstmethod (FIG. Skip mode information 5 bits 20) 0, split information 1,skip mode information 0, split information 1, skip mode information 1Maximum coding unit Skip mode information 5 bits skip first method (FIG.0, split information 1, 21) split information 1, split information 0,skip mode information 1

According to a split first method of Table 3, since split information ofa maximum coding unit having a depth of 0 is encoded to be ‘1’, splitinformation of a coding unit having a depth of 1 is encoded to be ‘1’,split information of a coding unit having a depth of 2 is encoded to be‘0’, and skip mode information of the coding unit having the depth of 2is encoded to be ‘1’, the data extractor 1520 may read four bits of skipmode information and split information in total. According to a skipfirst method of Table 3, since skip mode information of the maximumcoding unit having the depth of 0 is encoded to be ‘0’, splitinformation of the maximum coding unit having the depth of 0 is encodedto be ‘1’, skip mode information of the coding unit having the depth of1 is encoded to be ‘0’, split information of the coding unit having thedepth of 1 is encoded to be ‘1’, and skip mode information of the codingunit having the depth of 2 is encoded to be ‘1’, the data extractor 1520may read five bits of skip mode information and split information intotal. According to a maximum coding unit skip first method of Table 3,since skip mode information of the maximum coding unit having the depthof 0 is encoded to be ‘0’, split information of the maximum coding unithaving the depth of 0 is encoded to be ‘1’, split information of thecoding unit having the depth of 1 is encoded to be ‘1’, splitinformation of the coding unit having the depth of 2 is encoded to be‘0’, and skip mode information of the coding unit having the depth of 2is encoded to be ‘1’, the data extractor 1520 may read five bits of skipmode information and split information in total.

As described above with reference to FIGS. 19 through 21, by changing anorder of split information and skip mode information, a total bit numberof skip mode information about coding units according to depths may bevaried. For example, if a coding unit of an upper depth is predicted andencoded in a skip mode, since split information of a coding unit of alower depth does not need to be encoded, if there are many regionspredicted and encoded in a skip mode, it may be advantageous in terms ofa bit rate that skip mode information precedes split information.However, in an image with a small number of skip modes, it may beadvantageous in terms of a bit rate that split information precedes skipmode information.

Accordingly, a bit rate may be adjusted by adjusting an order of splitinformation and skip mode information according to characteristics of animage, a sequence, a data unit level such as a slice, a QP, and a slicetype. Also, like in the example explained with reference to FIG. 21where a skip first method is selected only for a maximum coding unit anda split first method is selected for coding units having depths otherthan the maximum coding unit, an order of split information and skipmode information may be changed according to depths.

In the exemplary embodiment described with reference to FIG. 18, skipmode information or split information is earlier read in units ofpictures. The apparatus 1400 of FIG. 16 and the apparatus 1500 of FIG.17 may variably determine an order in which skip mode information andsplit information are output or read according to a data unit, a depth,a QP, and a slice type according to a prediction direction without beinglimited to the exemplary embodiment of FIG. 18.

Also, split information and skip mode information may be combined andused as one piece of split and skip information. The apparatus 1400 ofFIG. 16 and the apparatus 1500 of FIG. 17 may use split and skipinformation that is assigned 1 bit for a combination of splitinformation and skip mode information having a high frequency ofoccurrence, and split and skip information that is assigned 2 bits for acombination having a low frequency of occurrence.

If split information precedes skip mode information, since splitinformation of a coding unit of a lower depth is immediately read whensplit information of a coding unit of a current depth is 1, a skip modeof a current coding unit is not read. Accordingly, three combinations,that is, split information 1, a combination of split information 0 andskip mode information 0, and a combination of split information 0 andskip mode information 1, may occur. For example, a frequency ofoccurrence of the combination of split information 0 and skip modeinformation 1 is the highest, the combination is assigned 1 bit, andeach of the split information 1 and the combination of split information0 and skip mode information 0 may be assigned 2 bits.

FIG. 22 is a flowchart illustrating a method of encoding a video byconsidering a skip and split order, according to an exemplaryembodiment.

In operation 1710, a picture is split into maximum coding units havingpredetermined maximum sizes.

In operation 1720, for each of coding units having a tree structure, anencoding mode about a coded depth to output an encoding result and acoding unit of the coded depth is determined by performing encodingbased on coding units according to depths, according to regions obtainedby hierarchically splitting the maximum coding unit as a depth deepens.

In operation 1730, information indicating an order of skip modeinformation and split information which is selectively determined forevery coding unit according to depths, information about the encodingmode including the skip mode information and the split information whichare arranged according to the determined order, and encoded video dataare output for every maximum coding unit.

Also, one piece of combined split and skip information obtained bycombining the split information and the skip mode information may beset. Also, a bit number of the corresponding split and skip informationmay be assigned based on a frequency of occurrence of a combination ofthe split information and the skip mode information.

FIG. 23 is a flowchart illustrating a method of decoding a video byconsidering a skip and split order, according to an exemplaryembodiment.

In operation 1810, a bitstream of an encoded video is received andparsed.

In operation 1820, information about an order of skip mode informationand split information of coding units according to depths is extractedfrom the bitstream, and according to the order of the skip modeinformation and the split information, information about a coded depthand an encoding mode and encoded video data are extracted according to amaximum coding unit from the bitstream.

Also, one piece of combined split and skip information obtained bycombining the split information and the skip mode information may beread. The method of decoding the video of FIG. 23 may read a combinationof the split information and the skip mode information based on thesplit and skip information that is discriminatively assigned based on afrequency of occurrence of a combination of the split information andthe skip mode information.

In operation 1830, encoded video data is decoded according to codingunits having a tree structure for every maximum coding unit of encodedvideo data based on the information about the coded depth and theencoding mode.

Exemplary embodiments can be written as computer programs and can beimplemented in general-use digital computers that execute the programsusing a computer readable recording medium. Examples of the computerreadable recording medium include magnetic storage media (e.g., ROM,floppy disks, hard disks, etc.) and optical recording media (e.g.,CD-ROMs, or DVDs). Moreover, one or more units of the apparatus 1400 andthe apparatus 1500 can include a processor or microprocessor executing acomputer program stored in a computer-readable medium, such as the localstorage 220

While exemplary embodiments have been particularly shown and describedabove, it will be understood by those of ordinary skill in the art thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope of the inventive concept as definedby the appended claims. The exemplary embodiments should be consideredin a descriptive sense only and not for purposes of limitation.Therefore, the scope of the inventive concept is defined not by thedetailed description of exemplary embodiments but by the appendedclaims, and all differences within the scope will be construed as beingincluded in the present invention.

What is claimed is:
 1. A method of decoding a video, the method comprising: receiving a bitstream of encoded video; extracting, from the bitstream, split information of a coding unit in a maximum coding unit of a picture; when the split information indicates a split for a current depth, splitting a coding unit of the current depth, independently from neighboring coding units, into coding units of a lower depth; and when the split information indicates a non-split for the current depth, determining at least one partition from the coding unit of the current depth and decoding the coding unit of the current depth by performing a prediction based on the at least one partition, wherein, when skip information for the coding unit of the current depth indicates a skip mode, the coding unit of the current depth is decoded by performing a prediction in the skip mode based on a partition having a size equal to a size of the coding unit of the current depth, and when the skip information for the coding unit of the current depth does not indicate the skip mode, the coding unit of the current depth is decoded by performing a prediction in a prediction mode indicated by prediction mode information obtained from the bitstream.
 2. The method of claim 1 wherein the split information indicates whether a corresponding coding unit is split into coding units of a lower depth.
 3. The method of claim 1, wherein, when the skip information for the coding unit of the current depth does not indicate the skip mode, the coding unit of the current depth is decoded by performing a prediction in a prediction mode indicated by prediction mode information, obtained from the bitstream, based on at least one partition having a size equal to or less than the size of the coding unit of the current depth.
 4. The method of claim 3, wherein the at least one partition having a size equal to or less than the size of the coding unit of the current depth is obtained from the coding unit of the current depth based on partition type information obtained from the bitstream.
 5. The method of claim 4, wherein the partition type information indicates one of a symmetric partition type and an asymmetric partition type. 